dt-bindings: watchdog: Add Qualcomm PM8916 watchdog

Document support for the Watchdog Timer (WDT) Controller in the
Qualcomm PM8916 PMIC module.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>